Not Applicable.
Not Applicable.
The present invention relates to machine tool cooling and to systems for supplying coolants to tools for cutting and other machine operations, and more particularly to distributors of cryogenic fluids for cooling tools mounted on a rotatable turret plate.
Examples of prior art devices and methods for cryogenic cooling tools in machining operations are disclosed in U.S. Pat. No. 5,761,974 (Wang, et al.) and U.S. Pat. No. 5,901,623 (Hong). These patents recognize that cryogenic cooling of tools for shaping parts by removing material is advantageous for its cleanliness, absence of the environmental impacts characterizing conventional cutting fluids, and improved tool life due to reduced tool wear rates.
However, the implementation of cryogenic cooling is difficult for tools mounted on rotationally indexing turret plates commonly used on machines like lathes or machining centers using a computerized numerical controller (CNC). Flowing from an external, pressurized source, the cryogen has to enter a machine carriage holding turret, which typically moves in two traverse directions (X-Z) and then proceeds to the specific tool that is engaged in a cutting operation at a given moment and has been mounted together with other tools on a multi-tool, rotationally indexing turret plate.
A turret-lathe coolant system disclosed in U.S. Pat. No. 5,265,505 (Frechette) is relatively simple to synchronize with the characteristic, rotational indexing of tools and may be retrofitted on the majority of modern CNC machines because the distribution valve and tubing are added on the top (or front) part of the turret. Unfortunately, the distributing valve, sealing and mounting mechanisms, as well as tubing used in the described apparatus, would certainly leak and eventually fail in a pressurized cryogenic fluid service, while the turret plate would suffer thermal shrinkage affecting dimensional accuracy of machined parts. The same comments apply to U.S. Pat. No. 5,862,833 (Perez), which discloses a somewhat improved sealing mechanism but requires a more complex retrofitting procedure and, because of an extensive conductive contact of the distributor with the turret plate, would result in significant dimensional inaccuracies during machining with a cryogenic fluid.
U.S. Pat. No. 4,164,879 (Martin) discloses a coolant system for a machine tool having a rotatable turret. The system includes a distributor mounted on the turret (coaxial with the axis of rotation of the turret) for directing coolant to a tool that has been indexed to the working position. The distributor includes a rotatable member (that rotates with the turret) in which a non-rotatable member is disposed. The rotatable member has a plurality of radially disposed passages which transmit coolant from the non-rotatable member to tool-receiving sockets on the turret. A check valve assembly in each socket and actuator members on selected tools selectably regulate the flow of coolant to tools in the working position. This coolant system would have many problems if used with cryogenic fluids, including moisture condensation and freezing of moving parts, leakage of low-viscosity cryogenic fluids through incompatible sealing components in which each material contracts thermally to a different degree while all elastomeric components become brittle, dimensional inaccuracy of an inadvertently cooled turret plate, etc.
Problems with dimensional accuracy and transfer efficiency characterizing valves distributing cryogenic fluids to cutting.tools in machining applications have been recognized in U.S. Pat. No. 5,509,335 (Emerson). The turret-plate distribution system taught in this patent features an actuated plunging valve which disconnects or connects tubing communicating with specific tools via a plunger seat according to the rotational indexing procedure called upon by a machining CNC program. While minimizing thermal shrinkage problems, this system requires a complete redesign of the turret, something highly impractical in a production environment, making quick retrofits impossible. Moreover, the plunging valve synchronization with the indexing action of the turret is not simple, and the reliability or life of the plunger seat is limited.
It is desired to have a distributor for delivering a liquid or two-phase stream of a cryogenic fluid (e.g., liquid nitrogen) to a specific tool mounted on a multi-tool turret and engaged in a machining operation, such as cutting.
It is further desired to have a distributor of a cryogenic fluid that can be easily installed on existing machines quickly and simply.
It is still further desired to have a cryogenic fluid distributor for cooling a machine tool that does not eliminate the capability of machining operations with conventional cutting fluids and does not preclude the option of simultaneously using a conventional fluid system and a cryogenic tool cooling system.
It is still further desired to have a cryogenic fluid distributor for cooling a machine tool that is affordable in the (low-margin driven) machining industries.
It is still further desired to have a distributor for delivering a cryogenic fluid which eliminates the possibility of cooling the tool-holding turret plate to prevent thermally induced dimensional inaccuracies in machined parts, and which operates in a liquid cryogen leak-free mode.
It is still further desired to have a distributor for delivering a cryogenic fluid which maximizes the use of thermally insulating materials and components, and which is characterized by a minimum thermal mass that can be cooled-down quickly so that only negligible, transient vapor choking would occur during warm start-ups of cryogenic flow, which may be required in the case of significantly interrupted machining operations.
It also is desired to have a distributor for delivering a cryogenic fluid which is reliable in operation, has no fast wearing parts, offers a simple synchronization with the rotational indexing of the turret plate, and never fails or seizes in a way that will damage machine tools, components, or parts being machined.
The present invention is a distributor of a cryogenic fluid for cooling at least one machining tool mounted on a rotatable turret plate. The cryogenic distributor can be retrofitted on conventional machine tools in such a way that the distributor does not eliminate the capability of machining operations with conventional cutting fluids.
A first embodiment of the invention includes a polymeric rotor, a metallic stator, and a self-sealing means. The polymeric rotor has a first coefficient of thermal expansion and a cavity within the rotor. The metallic stator has a first end, a second end, a first longitudinal axis, and a second coefficient of thermal expansion. A substantial portion of the stator is disposed in the cavity within the rotor, thereby forming at least one interface between the stator and the rotor. With regard to the self-sealing means, a difference between the first coefficient of thermal expansion and the second coefficient of thermal expansion results in at least one seal at the at least one interface between the stator and the rotor when the cryogenic fluid flows through at least a portion of the stator. In a variation of the first embodiment, the rotor may be disposed within a vapor jacket, thereby forming an annulus between the vapor jacket and the rotor.
Various cryogenic fluids may be used with the distributor. For example, the cryogenic fluid may be selected from the group consisting of cryogenic nitrogen, cryogenic argon, cryogenic carbon dioxide, cryogenic helium, and any combinations and mixtures thereof having a temperature less than or equal to minus 80xc2x0 Celsius. Flow of the cryogenic fluid to the distributor may be regulated by a flow control means, such as a flow control box.
In a preferred first embodiment, the distributor also includes a first metallic counter-shrink plate and a second metallic counter-shrink plate. The first metallic counter-shrink plate has an axis parallel to the first longitudinal axis and is mounted on the stator adjacent the second end of the stator within the cavity. The second metallic counter-shrink plate is mounted on the stator parallel to and above the first metallic counter-shrink plate within the cavity. The distributor also includes a first low-friction interface means between the stator and the first metallic counter-shrink plate, and a second low-friction interface means between the stator and the second metallic counter-shrink plate.
In another embodiment, the distributor also includes a post tube and a connecting arm. The post tube is attached to a turret carriage. The connecting arm has a first end connected to the stator and a second end connected to the post tube. In a variation of this embodiment, the length of the connecting arm is adjustable.
Another aspect of the present invention is a machine including at least one machining tool and a distributor of a cryogenic fluid for cooling the at least one machining tool as in the first embodiment discussed above.
In a second embodiment of the present invention, the distributor includes a conduit, a polymeric rotor, a metallic stator, and first and second metallic counter-shrink plates. The conduit has a first and a second end, the first end being in communication with a supply of the cryogenic fluid. The polymeric rotor has a first end, a second end, an outer wall between the first and second ends, an inner wall between the first and second ends, and a first longitudinal axis. The outer wall is substantially symmetrical about the first longitudinal axis, and the inner wall is substantially symmetrical about the first longitudinal axis and forms a substantially symmetrical cavity within the rotor between the inner wall and the first longitudinal axis. The rotor is rotatable about the first longitudinal axis and has at least one radial passage adjacent the second end of the rotor between the inner and outer walls of the rotor. Each radial passage is substantially equally spaced from a neighboring radial passage, substantially equidistant from the second end of the rotor, and has an inlet, an outlet and another longitudinal axis angularly spaced from the first longitudinal axis. A substantial portion of the metallic stator is disposed in the cavity within the rotor. The stator has a first end above first end of the rotor and a second end above the second end of the rotor. The stator has a first passage coaxial with the first longitudinal axis and a second passage having a second longitudinal axis angularly spaced from the first longitudinal axis. Each of the passages has an inlet and an outlet. The inlet of the first passage is in communication with the second end of the conduit; the outlet of the first passage is in communication with the inlet of the second passage; and the outlet of the second passage is adaptable to be in communication with the inlet of the at least one radial passage. The first metallic counter-shrink plate, which has an axis parallel to the first longitudinal axis, is mounted on the stator adjacent the second end of the stator within the cavity. The second metallic counter-shrink plate is mounted on the stator parallel to and above the first metallic counter-shrink plate within the cavity. In a variation of this embodiment, the another longitudinal axis of each radial passage is substantially perpendicular to the first longitudinal axis, and the second longitudinal axis of the stator is substantially perpendicular to the first longitudinal axis.
In a preferred second embodiment, the distributor also includes a first low-friction interface means between the stator and the first metallic counter-shrink plate, and a second low-friction interface means between the stator and the second metallic counter-shrink plate. The distributor also includes individual tubes in communication with and extending from each of the individual radial passages. Also, the second end of the rotor is connected to the turret plate. Preferably, the second end of the stator is spaced apart from the turret plate.